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<B><A HREF="dhclient.html">dhclient(8)</A></B>					      <B><A HREF="dhclient.html">dhclient(8)</A></B>


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<H2>NAME</H2><PRE>
       dhclient - Dynamic Host Configuration Protocol Client


</PRE>
<H2>SYNOPSIS</H2><PRE>
       <B>dhclient</B> [ <B>-p</B> <I>port</I> ] [ <B>-1</B> ] [ <B>-D</B> ] [ <B>-d</B> ] [ <I>if0</I> [ <I>...ifN</I> ] ]


</PRE>
<H2>DESCRIPTION</H2><PRE>
       The Internet Software Consortium  DHCP  Client,	dhclient,
       provides  a  means  for	configuring  one  or more network
       interfaces using the Dynamic Host Configuration	Protocol,
       BOOTP  protocol, or if these protocols fail, by statically
       assigning an address.


</PRE>
<H2>OPERATION</H2><PRE>
       The DHCP protocol allows  a  host  to  contact  a  central
       server which maintains a list of IP addresses which may be
       assigned on one or  more  subnets.    A	DHCP  client  may
       request	an  address  from this pool, and then use it on a
       temporary basis for communication on network.	The  DHCP
       protocol  also  provides  a mechanism whereby a client can
       learn important details about the network to which  it  is
       attached,  such	as  the location of a default router, the
       location of a name server, and so on.

       On startup, dhclient reads the <I>dhclient.conf</I> for  configu-
       ration instructions.   It then gets a list of all the net-
       work interfaces that are configured in the current system.
       For each interface, it attempts to configure the interface
       using the DHCP protocol.

       In order to keep track of leases across system reboots and
       server  restarts,  dhclient  keeps a list of leases it has
       been  assigned  in  the	dhclient.leases(5)   file.     On
       startup,  after	reading  the dhclient.conf file, dhclient
       reads the dhclient.leases file to refresh its memory about
       what leases it has been assigned.

       When a new lease is acquired, it is appended to the end of
       the dhclient.leases file.   In order to prevent	the  file
       from   becoming	arbitrarily  large,  from  time  to  time
       dhclient creates a new dhclient.leases file from  its  in-
       core   lease   database.    The	 old   version	 of   the
       dhclient.leases	file   is   retained   under   the   name
       <I>dhcpd.leases~</I>  until  the  next time dhclient rewrites the
       database.

       Old leases are kept around in  case  the  DHCP  server  is
       unavailable when dhclient is first invoked (generally dur-
       ing the initial system boot process).   In that event, old
       leases  from  the  dhclient.leases file which have not yet
       expired are tested, and	if  they  are  determined  to  be
       valid,  they are used until either they expire or the DHCP
       server becomes available.

       A mobile host which may sometimes need to access a network
       on  which  no  DHCP  server exists may be preloaded with a
       lease for a fixed address  on  that  network.	When  all
       attempts  to  contact  a DHCP server have failed, dhclient
       will try to validate the static lease, and if it succeeds,
       will use that lease until it is restarted.

       A  mobile  host	may also travel to some networks on which
       DHCP is not available but BOOTP is.   In that case, it may
       be  advantageous to arrange with the network administrator
       for an entry on the BOOTP database, so that the	host  can
       boot  quickly  on that network rather than cycling through
       the list of old leases.


</PRE>
<H2>COMMAND LINE</H2><PRE>
       The names of the network interfaces that  dhclient  should
       attempt to configure may be specified on the command line.
       If no interface names are specified on  the  command  line
       dhclient will identify all network interfaces, elimininat-
       ing non-broadcast interfaces if possible, and  attempt  to
       configure each interface.

       If  dhclient  should  listen  and transmit on a port other
       than the standard (port 68), the <B>-p</B>  flag  may  used.   It
       should  be  followed  by the udp port number that dhclient
       should use.  This is mostly useful for debugging purposes.
       If  the	<B>-p</B>  flag  is  specified, the client will transmit
       responses to servers at a port number  that  is	one  less
       than  the one specified - i.e., if you specify <B>-p</B> 68, then
       the client will listen on port 68 and transmit to port 67.
       Datagrams  that	must  go through relay agents are sent to
       the port number specified with the <B>-p</B> flag - if	you  wish
       to  use	alternate  port  numbers,  you must configure any
       relay agents you are using to use the same alternate  port
       numbers.

       Dhclient  will normally run in the foreground until it has
       configured an interface, and then will revert  to  running
       in the background.  To run force dhclient to always run as
       a foreground process, the <B>-d</B>  flag  should  be  specified.
       This  is useful when running dhclient under a debugger, or
       when running it out of inittab on System V systems.

       The <B>-D</B> flag causes <B>dhclient</B> to save the script it  creates
       for use in conjunction with <B>dhclient-script</B> in <I>/tmp.</I>

       The <B>-1</B> flag cause dhclient to try once to get a lease.  If
       it fails, dhclient exits.


</PRE>
<H2>CONFIGURATION</H2><PRE>
       The syntax  of  the  <B><A HREF="dhclient.conf.html">dhclient.conf(8)</A></B>  file  is	discussed
       seperately.


</PRE>
<H2>FILES</H2><PRE>
       <B>/etc/dhclient.conf</B>


</PRE>
<H2>SEE ALSO</H2><PRE>
       <B><A HREF="dhclient.conf.html">dhclient.conf(5)</A></B>, <B><A HREF="dhclient-script.html">dhclient-script(8)</A></B>


</PRE>
<H2>AUTHOR</H2><PRE>
       <B>dhclient(8)</B> has been written  for  the  Internet  Software
       Consortium  by Ted Lemon &lt;mellon@fugue.com&gt; in cooperation
       with Vixie Enterprises.	To learn more about the  Internet
       Software Consortium, see <B>http://www.vix.com/isc.</B>  To learn
       more about Vixie Enterprises, see <B>http://www.vix.com.</B>

       This client was substantially  modified	and  enhanced  by
       Elliot  Poger for use on Linux while he was working on the
       MosquitoNet project at Stanford.

       The current version owes much to Elliot's  Linux  enhance-
       ments,  but  was  substantially	reorganized and partially
       rewritten by Ted Lemon so as to use  the  same  networking
       framework  that	the  Internet  Software  Consortium  DHCP
       server uses.   Much system-specific configuration code was
       moved  into  a  shell  script  so that as support for more
       operating systems is added, it will not	be  necessary  to
       port  and  maintain  system-specific configuration code to
       these operating systems - instead, the  shell  script  can
       invoke the native tools to accomplish the same purpose.


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